Calculate Deltoid Perimeter: Given Area b² Square Centimeters

Question

Deltoid ABCD has an area of b2 b^2 cm².

What is its perimeter?

bbbbbbAAABBBCCCDDDEEE

Video Solution

Solution Steps

00:00 Calculate the perimeter of the kite
00:04 We'll use the formula for calculating kite area to find AC
00:07 (diagonal times diagonal) divided by 2
00:11 We'll substitute appropriate values and solve to find AC
00:16 Let's isolate AC
00:29 This is the length of AC
00:34 In a kite, the main diagonal intersects the secondary diagonal
00:48 In a kite, the diagonals are perpendicular to each other
00:53 We'll use the Pythagorean theorem in triangle AEB
00:57 We'll substitute appropriate values and solve to find AB
01:14 This is the length of AB
01:18 In a kite, adjacent sides are equal
01:26 Now we'll use the Pythagorean theorem in triangle CED
01:32 We'll substitute appropriate values and solve to find DC
01:54 This is the length of CD
01:58 Adjacent sides in a kite are equal
02:03 Let's mark all side lengths
02:16 The perimeter of the kite equals the sum of its sides
02:33 And this is the solution to the problem

Step-by-Step Solution

Let's find the perimeter of deltoid ABCD with given area b2 b^2 .

The formula for the area of a kite (or deltoid) is 12×d1×d2=b2 \frac{1}{2} \times d_1 \times d_2 = b^2 . Here d1 d_1 and d2 d_2 are the lengths of the diagonals of the kite.
Since 12×d1×d2=b2 \frac{1}{2} \times d_1 \times d_2 = b^2 , we rearrange to find d1×d2=2b2 d_1 \times d_2 = 2b^2 .

In a typical kite, each diagonal is the perpendicular bisector of the other; therefore, each side of the kite can be derived using diagonals through their perpendicular intersections.

If we take the segments created by the intersection of the diagonals, from the Pythagorean theorem, each pair of equal kite sides involves terms of the form a2+b2\sqrt{a^2 + b^2}, derived from these segments.

For example, if this kite is specifically structured such that the diagonals are split into segments where d1=b2d_1 = b\sqrt{2} and d2=b5d_2 = b\sqrt{5}, then:

  • Each pair of sides derived from these diagonal arrangements will also utilize (b22)2+(b52)2\sqrt{\left(\frac{b\sqrt{2}}{2}\right)^2 + \left(\frac{b\sqrt{5}}{2}\right)^2 }.
  • Therefore, the calculation leads us to b2+b5 b\sqrt{2} + b\sqrt{5} for each side.

Combining this for a total of four sides of the kite (two of each equal one):

Perimeter = 2(b2+b5)=2b(2+5) 2(b\sqrt{2} + b\sqrt{5}) = 2b(\sqrt{2} + \sqrt{5}) .

Thus, the perimeter of deltoid ABCD is 2b(2+5) 2b(\sqrt{2} + \sqrt{5}) .

Answer

2b(2+5) 2b(\sqrt{2}+\sqrt{5})